RE: Aim-TTi QPX750SP over current and over voltage protection behavior

michaelkellett — Sun, 19 Sep 2021 13:45:02 GMT

Nice information and review but I was very puzzled by your use of the term "foldback".

Most people seem to mean a current reducing protection system where the voltage starts to reduce when the current limit or trip point is reached and goes on reducing until the current hits some lower level.

https://www.electronics-notes.com/articles/analogue_circuits/power-supply-electronics/current-limiter-circuit.php

https://www.sciencedirect.com/topics/engineering/foldback-current-limiting

https://www.edn.com/foldback/

https://electronics.stackexchange.com/questions/2931/what-is-foldback-short-circuit-protection-in-a-power-supply

I don't think that the QPX750SP is behaving other than as a classic current limiting supply. This is not a bad thing, foldback protection on built in supplies is a good idea since it reduces the chances of thermal destruction but it's often unhelpful on the bench.

The Keysight SourceMeasure unit may not be the ideal load for this kind of test - I've usually found a big MOSFET and a selection of power resistors to be more helpful. (And mid range active loads like my Rigol DL3031A give mixed results too.) This is because a complex electronic dynamic load like an SMU or active load has it's own non ideal behaviour which can interact with the power supply.

So the 1.1V voltage at the output of the supply during current limiting in your "Test bridge data log of foldback test" graph is almost certainly an artefact of the SMU. If the load had been a 1R resistor you would have seen a different result.

RE: Aim-TTi QPX750SP over current and over voltage protection behavior

DAB — Sat, 18 Sep 2021 18:41:26 GMT

Good post.

DAB